<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>盒模型</title>
    <style>
        div {
            width: 200px;
            height: 200px;
            border:30px solid #ff705e;
            padding: 50px;
            margin-bottom:10px;
        }

        div:nth-child(2){
            box-sizing: border-box;
        }
    </style>
</head>
<body>
<div></div>
<div></div>
</body>
</html>